Superconducting controlled inductance circuits



Sept 27, 1966 c. R. cAsslDY ETAL 3,275,930

SUPERCONDUCTING CONTROLLED INDUCTANCE CIRCUITS Filed Feb. 13, 1963 4Sheets-Sheet l ATTORNEY Sept. 27, 1966 C. R. CASSIDY ETALSUPERCONDUCTING CONTROLLED INDUCTANCE CIRCUITS Filed Feb. 13, 1965 \JIl, il:

\, 'r I' @TSF-TTM 1500+ f f U U 56 4 Sheets-Sheet 2 Fig, 3A!! INVENTORS.

CARL R. cAssmY BY ALBERT J. MEYERHO (MAQ ATTORNEY Sept. 27, 1966 c. R.cAsslDY ETAL 3,275,930

SUPERCONDUCTING CONTROLLED INDUCTANCE CIRCUITS Filed Feb. 13, 1965 4Sheets-511861) 3 INVENTORS. CARL R. CASSIDY BY ALBERT J. MEYERHOFATTORNEY Sept- 27, 1966 c. R. cAssTDY ETAT. 3,275,930

SUPERCONDUCTING CONTHOLLED INDUCTANCE CIRCUITS Filed Feb. 13, 1963 4Sheets-Sheet 4 r /1\ INVENTORS.

CARL R. cAssToT To Y BY ALBERT J. MEYERH TT ATTORNEY United StatesPatent Office 3,275,930 Patented Sept. 27, 1966 3,275,930SUPERCONDUCTING CONTROLLED INDUCTANCE CIRCUITS Carl R. Cassidy, Hatboro,and Albert J. Meyerhoff, Wynnewood, Pa., assignors to BurroughsCorporation,

Detroit, Mich., a corporation of Michigan Filed Feb. 13, 1963, Ser. No.258,268 16 Claims. (Cl. 323-44) This invention relates tosuperconducting circuits and conductors and more particularly tosuperconducting circuits and conductors whose inductance is controlledby controlling the shielding qualities of a superconducting ground planeor shield.

Superconducting materials have been utilized to fabricate a variety ofcircuits and systems for performing functions similar -to thoseperformed by electronic and magnetic elements. Although superconductingcircuits are operated at temperatures in the vicinity of absolute zeroKelvin), this requirement is more than offset by their small physicalsize, rapid response, and low power consumption. Usually,superconductive circuits are operated at a fixed temperature at whichthe switchable elements, called gate conductors, normally exhibitsuperconductivity; that is, zero resistance to the flow of electricalcurrent. In order to switch the gate conductors into their normal orresistive state in which they present a resistance to the How ofelectrical current, a magnetic field of predetermined magnitude isapplied to the gate conductors. Generally, the required magnetic fieldis generated by means of current ow through conductors arranged inmagnetic field applying relationship with the gate conductors. In orderto reduce the power loss caused by current flow through the controlconductors, the control conductors are fabricated from a superconductingmaterial that remains superconducting in the presence of a magneticfield that causes the superconducting gate conductors to becomeresistive. That is, the superconducting control material has a highercritical magnetic eld than the superconducting gate material. Thecritical magnetic field for any superconducting material may be definedas the smallest magnetic field intensity that will cause thesuperconductor to switch to its normal or resistive state.

Heretofore in the prior art, each time a current was switched from onesuperconducting gate conductor path into another, energy was transientlydissipated due to 12R losses in the gate conductor. Even though therelaxation time for superelectrons is such that the superconductinggates can be switched from a superconducting state into a resistivestate in picoseconds (-12 seconds), the redistribution of current is atleast four or five orders of magnitude slower due to the inductance andresistance present in the circuit. This causes the current to continueto flow briefly through the resistive gate conductor and to dissipateenergy therein in the form of 12R losses. The sum of all such energylosses causes local heating which can result in faulty opeartion at highfrequencies.

These and other disadvantages of the prior art are materially reduced bythe present invention which discloses unique and novel superconductingconductors and circuits whose inductance is controlled by controllingthe shielding qualities of a superconducting ground plane or shield. Bycontrolling the inductance of superconducting conductors, current flowcan be rapidly switched from one superconducting conductor into anotherwithout causing either superconducting conductor to become resistive.This substantially eliminates the 12R energy losses associated withresistive current switching and also results in much lower switchingtimes.

Accordingly, an object of this invention is to provide a superconductorhaving a controlled inductance.

A further object of this invention is to provide a superconductor whoseinductance is controlled by controlling the shielding qualities of asuperconducting ground plane or shield.

Another object of this invention is to provide a superconducting currentpath having a controlled inductance whereby current may be rapidlyswitched from one superconducting path into another without producingsignificant I2R energy losses.

A still futrher object of this invention is to provide a high speedsuperconducting current switching circuit.

Another object of this invention -is to provide a high speed tree typesuperconducting current switching circuit.

Still another object of this invention is to provide a high speedcontrolled coupling circuit.

In accordance with a feature of the present invention there is provideda superconducting controlled inductance circuit which includes asuperconducting ground plane having a superconducting conductorassociated therewith. Means a-re provided for causing a portion of theground plane adjacent said superconducting gate conductor to becomeresistive thereby greatly increasing the inductance of thesuperconducting gate conductor.

In accordance with another feature of the present invention, asuperconducting controlled inductance circuit is provided which utilizesa ground plane of superconducting material having at least one openingthereon. A superconducting material having a critical magnetic eld lessthan the critical magnetic field of the ground plane material is locatedat the opening. At least one` superconducting current path is associatedwith the ground plane and at least a portion of this superconductingcurrent path is located adjacent the area ofthe opening. Magnetic fieldmeans are provided to cause the superconducting material located at theopening in said ground plane to become resistive thereby causing theinductance of the superconducting cu-rrent path to greatly increase.

In accordance with still another feature of the present invention acontrolled inductance circuit is provided which comprises means forcontrolling the inductance of a superconducting conductor and includes aground plane characterized as having at least one area that has acritical magnetic eld that is lower than the critical magnetic field forthe remaining area of the ground plane. At least one superconductingconductor, having a critical magnetic field greater than the area havingthe lower critical magnetic eld than the remaining area of said groundplane, is located adjacent said ground plane with at least a portion ofit being adjacent the area having a lower critical magnetic field.superconducting current means are provided for causing the area on theground plane having a lesser critical magnetic eld to become resistivethereby greatly increasing the inductance of the superconductingconductor.

In accordance with another feature of this invention a cryotroniccontrolled shield circuit is provided which comprises means forcontrolling the magnetic shield qualities of a ground plane and includesa ground plane of superconducting material. At least one superconductingconductor is positioned adjacent the ground plane for providing asuperconducting current path, and at least one superconducting controlconductor is also positioned adjacent the ground plane at an area whereit is desired to control the shielding qualities of the ground plane.Both :the current path super-conducting conductor and the controlsuperconducting conductor have a higher critical magnetic field than theground plane superconducting material. By applying a current to thecontrol superconducting conductor, a selected area of :the ground planelying adjacent said current path superconducting conductor is caused tobecome resistive thereby greatly increasing the inductance of thecurrent path superconducting conductor. Utilization means responsive tothe change in inductance in the current path superconducting conductoris coupled to said conductor.

In accordance with a still further feature of this invention a highspeed current switching circuit is provided which utilizes means forcontrolling the inductance of a superconducting conductor and includes aground plane of superconducting material having at least one areacharacterized as having a lower critical magnetic eld than the remainingarea of the ground plane. At least two parallel superconducting currentpaths are disposed adjacent the ground plane such that a portion of atleast one of the parallel current paths is adjacent the area on -theground plane having .the low critical magnetic ield. Superconductingmeans are provided for causing the ground plane area having the lowcritical magnetic field to become resistive thereby greatly increasingthe inductance of selected ones of the parallel current paths whichenables current to be rapidly switched from the selected superconductingcurrent path into the other.

In accordance with another feature of this invention a high speedswitching circuit is provided which utilizes a superconducting groundplane. A superconducting conductor tree circuit which provides aplurality of superconducting current paths and includes an apex and aplurality of branch current paths disposed adjacent the ground plane.Means are provided whereby the ground plane adjacent one or more of thesuperconducting branch current paths is caused to become resistivethereby increasing the inductance of the adjacent superconductingconductor which enables rapid switching of the current :through selectedones of the plurality of branch current paths.

Also, in accordance with a further feature of this invention acontrolled coupling transformer is provided which utilizes means forcontrolling the shielding qualities of superconducting shield andincludes a superconducting primary winding and a superconductingsecondary winding with at least a portion of the primary winding locatedadjacent a portion of the secondary winding. A shield of superconductingmaterial is located between the adjacent portions of the primary andsecondary windings. Superconducting current means are provided forcausing the superconducting shield Ato become resistive thereby enablingthe adjacent portions of said primary and secondary portions to be iluxlinked.

The exact nature of this invention as well as other objects and featuresthereof will be readily apparent from consideration of the followingdetailed description relating to the annexed drawings in which:

FIG. l illustrates one preferred embodiment of this invention;

FIG. 1A is a sectional view taken along line 1A of FIG. l which shows indetail ythe manner in which the device of FIG. l is fabricated;

FIG. 2A illustrates another preferred embodiment of this invention;

FIG. ZAA is a sectional view taken along line ZAA of FIG. 2A which showsin detail the marmer in which the device of FIG. 2A is fabricated;

FIG. 2B illustrates a modiiication of the device shown in FIG. 2A;

FIG. 2BB is a sectional View .taken along -line ZBB of FIG. 2B whichshows in detail the manner in which the device of FIG. 2B is fabricated;

FIG. 2C illustrates a further modification of the embodiment shown linFIG. 2A;

FIG. 2CC is a sectional view :taken along line 2CC of FIG. 2C whichshows in detail the manner in which the device of FIG. 2C is fabricated;

FIG. 3A illustrates another preferred embodiment of the presentinvention;

FIG. 3AA is a sectional view taken along line SAA of FIG. 3A which showsin detail the manner in which the device of FIG. 3A is fabricated;

FIG. 3B illustrates a modification of the device shown in FIG. 3A;

FIG. SBB is a sectional View taken along line SBB of FIG. 3B which showsin detail the manner in which the device in FIG. 3B is fabricated;

FIG. 3C illustrates a further modification of the devices shown in FIG.3A;

FIG. SCC is a sectional view taken along line SCC of FIG. 3C which showsin detail the manner in which the device of FIG. SC is fabricated;

FIG. 4 illustrates a utilization device which incorporates the deviceshown in FIGS. 2A, 2B and 2C;

FIG. 5 illustrates a superconducting bistable device fabricated inaccordance with the present invention;

FIG. 6 illustrates a superconducting tree type circuit fabricated inaccordance with the present invention;

FIG. 7 illustrates a controlled coupled superconducting transformerfabricated in accordance with the present invention; and

FIG. 7A is a sectional view taken along line 7A of FIG. 7 which shows indetail the manner in which the device of FIG. 7 is fabricated.

Referring now to the drawings, in which like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIGS. l and 1A an embodiment of the present inventionwhich includes a thin-film superconducting ground plane 11 which isdeposited on a suitable substrate 12 of material such as glass. Thesuperconducting ground plane 11 contains an opening 1S thereon which mayalso be characterized as a cut-out portion or discontinuity. Located atthis opening is a second type superconducting material 14 having a lowercritical magnetic field than the surrounding superconducting groundplane material 11. This second type superconducting material 14 may becharacterized as being located at, located adjacent, completelycovering, completely filling or located in proximity to the opening 1S.Covering the superconducting ground plane 11 and the second typesuperconducting material 14 is a layer of insulation 15 which may bedeposited thereon. A superconducting conductor 16 is deposited on thelayer of insulation and has at least a portion of its length adjacentthe second type superconducting material 14 located at the opening 13 inthe superconducting ground plane. Input terminal means 17 are located atone end of the superconducting conductor and output means 18 are locatedat the opposite end. The superconducting conductor 16 has a highercritical magnetic field than the second type superconducting materiallocated at the opening 13. For example, the superconducting conductor 16and the ground plane material 11 may be fabricated from lead and thesecond type superconducting material 14 located at the opening 1S may befabricated from tin.

Assume now that a current I is applied to the input terminal 17 andflows out of the output terminal 18, assume this current I generates amagnetic field around the superconducting conductor 16 the magnitude ofwhich does not exceed or equal the critical magnetic eld of thesuperconducting ground plane 11 material or the second typesuperconducting material 14. This prevents the magnetic eld frompenetrating the superconducting ground plane 11 material or the secondtype material 14. This causes .the magnetic field to be concentratedfairly uniformly between the superconducting conductor 16 and thesuperconducting ground plane 11 material and the second type material 14and is substantially negligible elsewhere. That is, the shieldingqualities of the superconducting ground plane 11 material and the secondtype material 14 does not permit the magnetic field around thesuperconducting conductor 16 to be symmetrical. This results in thesuperconducting conductor 16 having a very small inductance component.Assume now that the current I applied to the input terminal 17 graduallyincreasing thereby increasing the magnetic field density between thesuperconducting conductor 16 and the superconducting ground plane 11material and the second type material 14. At some point the density ofthe magnetic field located beneath the superconducting conductor 16 willequal the critical magnetic field for the second type critical magneticfield 14. When this occurs the second type superconducting material 14will assume an intermediate state, as described in more detail hereinbelow, which will permit further increases in magnetic flux to penetratethe second type material 14 in a manner as though the material 14 was ina resistive state. This causes the inductance of the superconductingconductor 16 to greatly increase. For example, it can be shown that thiswill cause the inductance of the superconducting conductor -to increasemore than a hundred times. Inasmuch as the superconducting conductor 16material and the superconducting ground plane 11 material have a highercritical magnetic field than the second type superconducting material14, they will remain superconducting.

When the second type superconducting material 14 enters the intermediatestate due to a critical magnetic field equal to or slightly larger thanthe critical magnetic field, the superconducting material 14 does notbecome completely resistive but may be characterized as containing areasof superconductivity intermingled with areas of resistivity. Under theseconditions the second type superconducting material 14 is believed tohave a high inductance component and very small 12R power losses. As themagnetic eld in the area of the second type material 14 is increased, itbecomes more resistive. For purposes of describing the present inventionthe term resistive will include an area which is partially resistive andpartially superconducting i.e. an intermediate state, as well as an areathat is entirely resistive. However, even when the material 14 becomesentirely resistive, the 12R losses remain very small. It is clear thenthat the device of FIG. 1 illustrates a superconducting controlledinductance circuit having no significant 12R losses.

Referring now to FIG. 2A and FIG. 2AA, there is shown a modification ofthe device shown in FIGS. 1 and 1A, comprising a continuoussuperconducting ground plane 21 material which is deposited on asuitable substrate 22 such as glass. A layer of insulation 23 covers theground plane 21 material and deposited upon this layer of insulation 23is a superconducting substantially U- shaped control conductor 24 havingan input terminal 25 to which a control current IC may be applied. Thebase of the U-shaped control conductor 24 is covered with a layer ofinsulation 26 and deposited on this insulation and adjacent to the baseof the control conductor 24 is a superconducting conductor 27 having aninput terminal 28 and an output terminal 29. Both the superconductingconductor 27 and the superconducting control conductor 24 are fabricatedfrom a material having a higher critical magnetic field than thecontinuous ground plane 21 material. For example, the ground plane 21material may be fabricated from tin, and the superconducting conductor27 and the control conductor 24 may be fabricated from lead.

The operation of the device shown in FIGS. 2A and 2AA is such that aslong as the continuous ground plane 21 remains superconducting thesuperconducting conductor 27 has a very small inductance component.However, whenever the current IC applied to the control con` ductor 24creates a magnetic field beneath it that exceeds the critical magneticfield of the ground plane 21, the ground plane material located adjacentthe control 24 becomes resistive. Inasmuch as a portion of thesuperconducting conductor 27 is located adjacent the control conductor24, the portion of the ground plane 21 adjacent the control conductor 24becomes resistive and greatly increases the magnitude of the inductanceof the superconducting conductor 27. As mentioned hereinabove, theground plane becoming resistive causes the inductance of thesuperconducting conductor 27 to increase more than a hundred times. Itis clear fthen that by controlling the magnitude of the` current ICapplied to the control conductor 24 the inductance of thesuperconducting conductor 27 may be controlled.

FIGS. ZB and ZBIB illustrate a modification of the device shown in FIGS.2A and ZAA wherein the superconducting conductor 27 whose inductance isto be controlled is located between the ground plane 21 and the controlconductor 24. FIGS. 2C and 20C illustrate a modification of the deviceshown in F'IGS. 2A and ZAA wherein the ground plane 21 is locatedbetween the control conductor 24 and the superconducting conductor 27Iwhose inductance is to be controlled. The devices shown in FIGS. 2Athrough 2CC operate equally Well and which one is utilized is a matterof choice. Inasmuch as the magnetic field generated by passing a currentthrough a superconducting conductor, such as the control conductor 24,is inversely proportional to the width of the superconducting conductor,the legs of the U-shaped control conductor 24 may be made wider than thebase portion thereby limiting the area of the ground plane 21 which iscaused to go resistive to that adjacent the superconducting conductor2'7.

Referring now to FIG. 4, there is illustrated in schematic form abistable device which uti-lizes the device of FIGS. 2A and 2AA torapidly switch current in a superconducting circuit without producingsignificant 12R energy losses. 'Ihe device comprises a ground plane 42upon which are deposited two parallel superconducting current paths 43and 45 each of which utilizes the device shown in FIGS. 2A and ZAA. Acurrent I is applied to the terminal 46 and leaves the circuit by way ofthe terminal 47. Whenever each of the parallel paths 43 and 45 aresuperconducting, the current I divides equally between them as long astheir inductances are equal. Assume now that the current I is flowingthrough both the superconducting current paths 43 and 45 and it isdesired to switch substantially all of the current I into the right handcurrent path 45. This can be accomplished by applying a control currentIC to the control conductor 48 which causes a portion of the groundplane 42 adjacent the left hand superconducting current path 43 tobecome resistive. This greatly increases the inductance of this currentpath 43 and substantially all of the current I flowing in this currentpath will be substantially instantaneously switched to the right handcurrent path 45. In order to have the current switching as rapid aspossible and therefore the change of inductance as rapid as possible, arectangular or square pulse of current IC is applied to the controlconductor 48.

Upon termination of the current pulse Ic the inductance of the currentpath 43 again becomes very small. However, since there can be no netflux change in a superconducting circuit, substantially all of thecurrent I will continue to flow in the superconducting current path 45.If a pulse of current IC is now applied to the control conductor 49causing a portion of the ground plane 42 beneath it to become resistive,thereby causing the inductance of the current path 45 to increasegreatly, substantially simultaneously most of the current I will beswitched to the superconducting current path 43 which no'w has a verysmall inductance. It is clear from the above that very rapid switchingof current in a superconducting circuit is accomplished withsubstantially no 12R losses because the entire circuit remainssuperconducting. As mentioned `herein above, the 12R losses in the areaof the ground plane caused to become resistive are negligible.

Due to the Eiiux which may be trapped in the areas on the ground plane4Z caused t-o become resistive, the number of times the current I may beswitched between the two current paths 43 and `445 may be limited.Accordingly, after the current I has been switched a few times, it maybe interrupted until the control conductors 48 and 49 are againactivated to select a new current path at which time the current I mayagain be applied and switched `between the two parallel current paths.Alternatively, selected ones of the control conductors 48 and 49 may beactivated before the current I is applied so that upon application ofthe current I it will be follow a predetermined path. Each -time it isdesired to change this current path, the current I may be interruptedlong enough to activate the appropriate control conductors 48 and 49after which the current I may again be applied and it will Iilow throughthe selected current path.

Referring now FIG. 3A and FIG. SAA, there is illustrated anotherembodiment of the present invention which comprises a discontinuousground plane 32 which is deposited on a suitable substrate 33 such asglass. Located at the opening 34 or discontinuity onthe ground plane 32is a second type of superconducting material 35 which can becharacterized as having a lower critical magnetic Iiield than theremaining ground plane 32 material. That is, the ground plane 32materia-l and the second type superconducting 35 material correspond tothe ground plane 11 and the second type superconducting material 14illustrated in conjunction with FIGS. l and 1A. A layer of insulation 36is deposited over the discontinuous ground plane and deposited upon thislayer of insulation is a substantially U-shaped superconducting controlconductor 37 the base of which lies adjacent the second typesuperconducting material 35. A layer of insulation 38 is deposited overthe base portion of the control conductor 37. A superconductingconductor 39 whose inductance is to be controlled is then deposited suchthat at least a portion of its length lies adjacent the base portion ofthe control conductor 37 and the second type superconducting material3'5. The superconducting conductor 39 and the control conductor 37 arefabricated from material having a higher critical magnetic field thanthe second type superconducting material 35. For eX- ample, if thesecond type superconducting material 35 is tin, llead may be used tofabricate the control conductor `37, the discontinuous ground plane 32,and the conductor 39.

As long as the second type superconducting material rem-ainssuperconducting, the inductance of the conductor 39 remains very small.Whenever it is desired to increase this inductance (this change ininductance can be greater than a hundred times), a control current IC isapplied to the control conductor 37 which creates a magnetic eld ofsufcient density to cause the second type superconducting material 35 tobecome resistive. The magnitude of the magnetic field is arranged to vbesuch that although it has a magnitude suflicient to cause the secondtype superconducting material 3S to become resistive, it is not ofsuicient magnitude to cause the discontinuous :ground plane 32 materialor the superconducting conductor 39 material or the control conductor 37material to become resistive.

For many applications of the device shown in FIGS. 3A and BAA thecurrent llowing in the superconducting conductor 39 may be in -adirection such that it either aids or opposes the current Ic applied tothe control conductor 37. It i-s therefore necessary that the magnitudeof the control current IC be of sufficient magnitude to render thesecond type superconducting material 35 resistive whenever the current Iowing in the superconducting conductor V39 is in opposition to it.Whenever the current I in the superconducting conductor 39 and thecontrol current Ic the oontrol conductor 37 aid each other other, theircombined magnetic field should be of such a value to be insuflicient tocause the discontinuous ground plane 32, the superconducting conductor39 or the control conductor 37 to become resistive. The current ICapplied to the control conductor 37 can be either D.C. or A.C. dependingupon the use to which the device of FIGS. 3A and 3AA is put. It is clearthen that the inductance of the superconducting conductor 39 may becontrolled by Ithe current IC applied to the control conductor 37.

FIGS. 3B and 3BB illustrate a modication of the clevice shown in FIGS.3A and 3AA wherein the superconducting oonductor 39 whose inductance isto be controlled is located between the control conductor 37 and theground plane materials 32 and 35. FIGS. 3C and SCC illustrate amodification of the device shown in FIGS. 3A and 3AA wherein thesuperconducting ground plane materials 32 and 35 are located between thesuperconducting conductor 39 andthe control conductor 37 FIG. 5illustrates in detail a high speed current switching circuit, similar tothat shown in FIG. 4 in schematic form, which utilizes the change ininductance of a superconducting current path to rapidly switch current.The circuit comprises a ground plane 52 which is deposited on a suitablesubtrate material 53. The ground plane 52 is characterized as having twoareas 54 each having a lower critical magnetic ield than the remainingarea of the ground plane 52. A layer of insulation 55 covers the groundplane and deposited upon the insulation 55 adjacent the two areas 54 aresubstantially U-shaped control conductors 61 and 62 having their baseportions adjacent the areas having the low critical magnetic eld. Alayer of insulation 56 covers the base portion of each of the controlconductors 61 and 62. Two parallel superconducting current paths 57 and58 are then deposited such that a portion of each parallel current pathis adjacent an area 54 having a low critical magnetic field.

In the absence of a control current IC in either of the controlconductors 61 4and 62, a current I applied to the terminal 59 willdivide equally between ythe two parallel current paths S7 and 58 vandleave the terminal 60 as long as the inductance of the two current pathsS7 and 58 are equal. By applying a pulse of current IC to the controlconductor 61 substantially all of the current I will be simultaneouslyswitched to the other superconducting current path 58. This occursbecause when the associated area 54 beneath the control 61 having a lowcritical magnetic field is caused to become resistive, the inductance ofthe superconducting current path 57 greatly increases becoming very muchlarger than the inductance in the other superconducting current path 58.Since the current I divides between the two parallel current branches 57and 58 inversely as to their inductances and since the inductance of thesuperconducting current path S7 is very much larger than the inductanceof the other superconducting current path 58, substantially all of thecurrent I will ilow through the superconducting current path 58. Sincethere is no resistance in the circuit, the current switching time is notdelayed by any L/R time constants. The current switching time isdependent upon the time it takes to increase the inductance of thesuperconducting conductor S7 from its very low value to its very highval-ue. By applying a rectangular or square pulse of current to thecontrol conductor 61, this change in inductance occurs substantiallysimultaneously causing the current switching time to be very small.

FIG. 6 illustrates a high speed switching circuit similar to that shownin FIG. 5 but comprising a tree type circuit instead of a parallelcurrent path circuit as shown in FIG. 5. Referring to FIG. 6 there isshown a ground plane 63 having -a plurality of :areas 67 characterizedas having a lower critical magnetic field than the remaining area of theground plane. A superconducting tree circuit having a plurality ofcurrent paths including an apex 68 and a plurality of branches 69 liesadjacent the ground plane such that a portion of each superconductingbranch current path lies adjacent one of the areas having a low criticalmagnetic field. A superconducting control conductor 70 is associatedwith each of the areas having a low critical magnetic field for causingthese areas to become resistive thereby greatly increasing ltheinductance of the adjacent superconducting current path. It will beclear to those skilled in the art that a current I applied to the apex68 of the tree circuit can be routed to any one of the output terminals71 by applying a control current to appropriate ones of the controlconductors 70. Whenever it is desired to have the current I leave via adifferent output terminal 71, it is only necessary to energize theappropriate control conductors 70 and the current I will be switchedvery rapidly without producing any 12R power losses inasmuch as thesuperconducting tree circuit will remain always superconducting. As willbe obvious to those skilled in the art, appropriate layers of insulation(not shown) must necessarily separate the various superconductingelements described above.

Due to the ux which may become trapped in the areas 67 on the groundplane 63 caused to become resistive, the number of times the current Imay be switched around the tree circuit of FIG. 6 may be limited.Accordingly, after the current I has been switched a few times, it maybe interrupted until the control conductors 70 are activated to producea new current path at which time the current I may again be applied andswitched around the tree circuit. Alternatively, selected ones of thecontrol conductors 70 may be activated before the current I is A appliedso that upon application of the current I it will follow a predeterminedpath. Each time it is desired to change this path, the current I may beinterrupted long enough to activate the appropriate control conductors70 after which the current I may again be applied and it will ow throughthe selected current path.

FIGS. 7 and 7A illustrate a control coupling transformer which comprisesa superconducting primary winding 74 and a closed loop superconductingsecondary winding 75. At least a portion of the primary winding 74 islocated adjacent at least a portion of the secondary winding 75 asillustrated in FIG. 7. Located between the adjacent portions of theprimary and secondary windings is a superconducting shield 76 which,While superconducting, prevents iiux coupling between the primary andsecondary winding. Also located between the adjacent portions of theprimary 74 and secondary 75 windings is a control conductor 77. Theentire transformer is deposited upon a superconducting ground plane 78having an opening 79 thereon with the portion of the secondary Windingadjacent the primary winding being located adjacent this opening .asillustrated in FIG. 7A. As will be obvious to those skilled in the art,appropriate layers of insulation (not shown) must necessarily separatethe various superconducting elements described herein Iabove.

The operation of the transformer is such that in the absence of acontrol current IC applied to the control conductor 77, thesuperconducting shield 76 remains superconducting and therefore preventsany liux linkage between the secondary 75 and the primary 74 in responseto a current I owing through the primary 74 winding. Whenever it isdesirable to ux couple the primary winding 74 to the secondary winding75 thereby inducing a current in the closed loop secondary winding 75,it is only necessary to apply a control current IC to the controlconductor 77 of suiicient magnitude to lcreate a magnetic eld ofsuiiicient density that causes the superconducting shield 76 to becomeresistive. Whenever the superconducting shield 76 becomes resistive,flux coupling exist between the primary 74 and the secondary 75 ibecausethe magnetic field created by the primary current I can now pass throughthe previously superconducting shield 76.

It is clear then that the device illustrated in FIGS. 7

and 7A is a controlled coupling transformer and that the coupling iscontrolled by controlling the resistance of a superconducting shield.For proper operation of this device, the superconducting shield 76material has .a lower critical magnetic eld than the ground plane 78material, the control 77 material, the primary winding 74 material, andthe secondary Winding 75 material.

Superconducting circuits and conductors have been described whoseinductance is controlled by controlling the shielding qualities of asuperconducting ground plane or shield. By causing a portion of a groundplane .adjacent a superconducting conductor to become resistive, themagnetic held around a current carrying superconducting `conductorbecomes symmetrical and greatly increases the inductance of thesuperconducting conductor. High speed current switching circuits and acontrol coupling transformer have been described which utilize thistechnique together with various structures for controlling theinductance of a superconducting path.

What is claimed is:

1. A superconducting circuit comprising:

a ground plane of continuously superconducting material having at leastone cut-out portion,

a discontinuously superconducting material having a critical magneticfield less than the critical magnetic field of said ground planesuperconducting material located at said -cut-out portion,

at least one current path of continuously superconducting materialassociated with said ground plane, and

at least a portion of said current path superconducting material alsolocated at the area of said cut-out portion.

2. A superconducting circuit comprising:

a ground plane of first type superconducting material having at leastone opening thereon,

a second type super-conducting material located adjacent said opening,

at least one current path of continuously superconducting materialassociated with said ground plane such that at least a portion of saidcurrent path is adjacent said second type material, and

said second type material having a lower critical magnetic ield thansaid ground plane and said current path material.

3. A c-ontrolled inductance circuit comprising:

means for controlling the inductance of a continuously superconductingconductor including;

a superconducting ground plane characterized Ias having at least onearea `that has a critical magnetic field which is lower than thecritical magnetic iield for the remaining area of said ground plane,

at least one continuously superconducting conductor whose inductance isto be controlled associated with said ground plane,

at least a portion of said superconducting conductor being adjacent saidground plane area having a lower critical magne-tic eld,

means associated with said ground plane area having a lower criticalmagnetic eld for causing said area to become resistive therebyincreasing the inductancek of said continuously superconducting=conductor, and

means connected to said superconducting conductor for utilizing saidincreased inductance.

4. A controlled inductance circuit comprising:

means -for controlling the inductance of a continuously superconductingconductor including:

a ground plane characterized as .having at least one area that has acritical magnetic field which is lower than the critical magnetic fieldfor the remaining area of said ground plane,

at least one continuously superconducting conductor whose inductance isto be controlled associated with said ground plane and having a criticalmagnetic field greater than said ground plane area having a lowercritical magnetic field,

at least a portion of said continuously superconducting conductor beingadjacent said ground plane having a lower critical magnetic field,

magnetic field means associated with said ground plane area having alower critical magnetic field for causing said area to become resistivethereby increasing the inductance of said continuously superconductingconductor, and

utilization means coupled to said superconducting conductor andresponsive to said increased inductance.

5. A cont-rolled inductance circuit comprising: means for controllingthe inductance of a superconducting conductor including;

a ground plane characterized as having at least one area having a lowercritical magnetic field than the remainder of the ground plane,

at least one continuously superconducting conductor Whose inductance isto be controlled associated with said ground plane,

at least a portion of said continuously superconducting conductor beingadjacent said area,

continuously superconducting current means associated with said area forcausing the area to become resistive thereby increasing the inductanceof said superconducting conductor.

6. A superconducting controlled inductance circuit comprising:

means for cont-rolling the inductance of a continuously superconductingconductor including;

a ground plane of superconducting material having at least one areacharacterized as having a lower critical magnetic field than theremaining arca of said ground plane,

at least two parallel continuously superconducting current pathsadjacent said ground plane such that a portion of at least one saidparallel current path is adjacent said ground plane area hav- A ing alower critical magnetic field,

each said parallel superconducting current path having a higher criticalmagnetic field than said ground plane area having a lower criticalmagnetic field, and

means associated with at least one said parallel superconducting currentpath for causing at least a portion of said ground plane area having alower critical magnetic field to become resistive thereby increasing theinductance of selected ones of said continuously superconductingparallel current paths.

7. The combination defined in claim 6 wherein said -means associatedwith at least one said continuously superconducting parallel currentpath includes supercon- Iducting current means having a larger criticalmagnetic field than said area having a lower critical magnetic fieldthan the remaining area of said ground plane.

8. The combination defined in claim 6 wherein said means associated withat least one said continuously superconducting parallel current pathincludes magnetic field means.

9. A superconducting circuit comprising: means for controlling theinductance of a superconductor including;

a ground plane of superconducting material having at least one areacharacterized as having a lower critical magnetic field than theremainder of the ground plane, at least two spaced apart continuouslysuperconducting conductors providing parallel superconducting currentpaths adjacent said ground plane such that a portion of each saidparallel current path is adjacent a ,Said arca,

each said continuously superconducting conductor having a highercritical magnetic field than said areas, and

means associated with each said continuously superconducting conductorfor causing at least one of said areas to become resistive therebyincreasing the inductance of selected ones of said continuouslysuperconducting conductors.

l0. A combination defined in claim 9 wherein said means associated witheach said continuously superconducting conductor includes magnetic fieldmeans.

11. A combination claimed in claim 9 wherein said means associated witheach said continuously superconducting conductor includes continuouslysuperconducting current means.

12, A combination defined in claim 10 wherein said magnetic field meansincludes a superconducting material having a larger critical magneticfield than said area.

13. A superconducting circuit comprising:

means for controlling the inductance of a continuously superconductingconductor including;

a ground plane having a plurality of areas characterized as having alower critical magnetic field than the remainder of the ground plane,

a superconducting conductor tree circuit providing a' plurality ofcontinuously superconducting current paths including a apex and aplurality of lbranch current paths adjacent said ground `plane,

at least a portion of each said superconducting branch current pathsadjacent one of said areas, and

means associated with each said area for causing selected ones of saidareas to become resistive thereby increasing the inductance of selectedbranch current paths.

14. A superconducting circuit providing:

means for controlling the inductance of a continuously superconducingcurrent path including;

a continuously superconducting primary winding,

a continuously superconducting secondary windlng,

at least a portion of said primary Winding located adjacent at least aportion of said secondary winding,

a shield of superconducting material located between the adjacentportions of said primary and secondary windings, and

means for causing said superconducting shield to Abecome resistivethereby enabling the adjacent portions of said primary and secondarywinding t0 be flux linked.

15. The combination defined in claim 14 wherein said superconductingshield has a lower critical magnetic field than said superconductingprimary and secondary windmg.

16. superconducting controlled inductance circuit comprising:

means for controlling the inductance of a superconductor including;

a continuously superconducting primary winding,

a continuously superconducting closed loop secondary winding,

at least a portion of said primary winding located Aadjacent at least aportion of said secondary winding,

a shield of superconducting material associated with the adjacentportions of said primary and secondary windings for preventing fluxcoupling between said primary and secondary winding,

said superconducting shield having a lower critical magnetic field thansaid superconducting primary and secondary windings, and magnetic fieldmeans associated with said superconducting shield for causing saidshield to become resistive thereby enabling said adjacent portions ofsaid continuously superconducting primary and secondary to be uxcoupled.

References Cited bythe Examiner UNITED STATES PATENTS 2,944,211 7/1960Richards 323-94 2,946,030 7/1960 Slade 336-155 2,989,714 6/1961Parketal.- 307-885 3,098,967 7/1963 Keek 323-94 10 '3,145,310 8/1964Bertuch et al 307-88.5 3,184,674 5/1965 Gamin 323-44 3,185,862 5/1965Beesley 307-885 14 3,191,063 6/1965 Ahrons 307-885 3,207,921 9/1965Ahrons 307-885 3,214,679 10/ 1965 Richards 323-44

14. A SUPERCONDUCTING CIRCUIT PROVIDING: MEANS FOR CONTROLLING THEINDUCTANCE OF A CONTINUOUSLY SUPERCONDUCTING CURRENT PATH INCLUDING; ACONTINUOUSLY SUPERCONDUCTING PRIMARY WINDING, A CONTINUOUSLYSUPERCONDUCTING SECONDARY WINDING, AT LEAST A PORTION OF SAID PRIMARYWINDING LOCATED ADJACENT AT LEAST A PORTION OF SAID SECONDARY WINDING, ASHIELD OF SUPERCONDUCTING MATERIAL LOCATED BETWEEN THE ADJACENT PORTIONSOF SAID PRIMARY AND SECONDARY WINDINGS, AND MEANS FOR CAUSING SAIDSUPERCONDUCTING SHIELD TO BECOME RESISTIVE THEREBY ENABLING THE ADJACENTPORTIONS OF SAID PRIMARY AND SECONDARY WINDING TO BE FLUX LINKED.